Cutting insert

ABSTRACT

A cutting insert which is excellent in both cutting edge strength and chip evacuation is provided. A corner edge of the cutting insert is formed in an arc shape. In a direction perpendicular to a rotation axis of a body, a width of the corner edge is 40% or more and 50% or less of a width of the cutting insert. An upper surface has a negative land which is formed along a cutting edge and has a negative angle. The angle of the negative land increases from one end, which is connected to an inner cutting edge, of both ends of the corner edge toward the other end.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese PatentApplication No. 2020-039878, filed on Mar. 9, 2020 and Japanese PatentApplication No. 2019-079331, filed on Apr. 18, 2019, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND Field

The present invention relates to a cutting insert used for cutting, andmore particularly to a cutting insert attached to an indexable cuttingtool used for milling.

Description of Related Art

There is a desire to design a cutting edge having high strength withwhich a work material having high hardness can be machined.

SUMMARY

When an axial rake angle (axial rake) is set to be a negative angle(negative), the rake angle reduces at both a tip and an outercircumference of a milling tool, and cutting edge strength can increase.On the other hand, when the axial rake angle is set to be a negativeangle, chips are easily discharged toward a lower side (the tip side) ofthe milling tool, and clogging of chips, rubbing of the chips on a worksurface, and the like easily occur. On the other hand, when a rakesurface of a cutting insert is formed into a flat surface and the axialrake angle is set to be a positive angle, a true rake angle increases asa distance from the tip of the milling tool increases, and the cuttingedge strength decreases.

An object of the present invention is to provide a cutting insert whichis excellent in both cutting edge strength and chip evacuation.

A cutting insert according to an aspect of the present invention is acutting insert which is mounted on a body rotating about a rotation axisand constitutes an indexable cutting tool together with the body. Thecutting insert includes a lower surface mounted on a seat surface of thebody, an upper surface opposite to the lower surface, and acircumferential surface connecting the lower surface to the uppersurface. A cutting edge is formed at a ridge line at which the uppersurface and the circumferential surface intersect. The cutting edge hasan inner cutting edge and a corner edge. The corner edge is formed at aposition farther from the rotation axis than the inner cutting edge andis connected to the inner cutting edge. The corner edge is formed in anarc shape in a plan view seen from a direction facing the upper surface.In a direction perpendicular to the rotation axis, a width of the corneredge is 40% or more and 50% or less of a width of the cutting insert.The upper surface has a negative land which is formed along the cuttingedge and has a negative angle, and a flat surface which is connected tothe negative land and parallel to the lower surface. The angle of thenegative land increases from one end, which is connected to the innercutting edge, of ends of the corner edge toward the other end.

According to this aspect, the angle of the negative land formed adjacentto the corner edge has a smaller value at a portion located closer tothe tip of the milling tool. By providing the negative land of which aland angle gradually changes to a positive side toward a side away fromthe tip of the milling tool, the cutting edge strength can be enhancedwhile the chip evacuation is be improved.

In the above aspect, the cutting edge of the cutting insert further hasa linear wiper edge which is connected to the corner edge and parallelto the rotation axis. In the ridge line in the wiper edge, the linearridge line of the upper surface preferably intersects the wiper edge atan obtuse angle.

According to this aspect, since the wiper edge wipes a machined surfaceof the corner edge, roughness of the machined surface is improved. Inthe linear ridge line, since the linear ridge line of the upper surfaceand the wiper edge intersect at an obtuse angle, the linear ridge linecoming into contact with a work surface and deteriorating roughness ofthe machined surface can be prevented in advance.

In the above aspect, it is preferable that the cutting insert furtherinclude a through hole penetrating from the upper surface to the lowersurface, and when the upper surface is viewed from above, a proportionof the flat surface in an area excluding the through hole from the uppersurface is preferably 90% or more.

When there is unevenness on the upper surface, restrictions on how tomove a grindstone when grinding the cutting insert occur. According tothis aspect, since most of the upper surface is formed of a flatsurface, grinding is easily performed. It can be manufactured withhigher precision than a cutting insert having a chip breaker or the likeformed on the upper surface.

According to the present invention, it is possible to provide a cuttinginsert which is excellent in both cutting edge strength and chipevacuation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing an example of a cutting insertaccording to one embodiment of the present invention;

FIG. 2 is a perspective view of the cutting insert shown in FIG. 1 seenfrom below;

FIG. 3 is a top view of the cutting insert shown in FIG. 1 seen fromabove;

FIG. 4 is a side view of the cutting insert shown in FIG. 1 seen from acircumferential surface (a second side surface part);

FIG. 5 is a side view of the cutting insert shown in FIG. 1 seen from acircumferential surface (a second front surface part);

FIG. 6 is a cross-sectional view along line VI-VI in FIG. 3;

FIG. 7 is a cross-sectional view along line VII-VII in FIG. 3;

FIG. 8 is a perspective view showing an example of an end mill providedwith the cutting insert of the present embodiment;

FIG. 9 is a diagram of a tip part of the end mill shown in FIG. 8 seenfrom an upper surface side of the cutting insert; and

FIG. 10 is a diagram of the tip part of the end mill shown in FIG. 8seen from a direction parallel to a rotation axis of a body.

DETAILED DESCRIPTION

A preferred embodiment of the present invention will be described withreference to the accompanying drawings. Also, in each of the drawings,components denoted by the same reference numerals have the same orsimilar configurations. In a cutting insert 10 of the present invention,whole parts of cutting edges 10 f, 10 g, and 10 m are disposed at asubstantially constant height from a lower surface 10 b (see FIGS. 4 and5). A negative land 10 q provided along a corner edge 10 f is formedsuch that an angle thereof increases from θ1 to θ2 from one end 12,which is connected to an inner cutting edge 10 g, to the other end 13(see FIGS. 6 and 7). By providing the negative land of which a landangle gradually changes to a positive side toward a side away from a tipof a milling tool, cutting edge strength can be enhanced while chipevacuation can be improved. Hereinafter, each configuration will bedescribed in detail with reference to FIGS. 1 to 10.

FIGS. 1 and 2 are perspective views showing an example of the cuttinginsert 10 according to one embodiment of the present invention. As shownin FIGS. 1 and 2, the cutting insert 10 includes an upper surface 10 a,the lower surface 10 b opposite to the upper surface 10 a, andcircumferential surfaces 10 d, 10 d′, 10 e, and 10 e′ connecting theupper surface 10 a to the lower surface 10 b.

The circumferential surfaces include a pair of substantially flat sidesurfaces 10 d and 10 d′ and a pair of front surfaces 10 e and 10 e′providing connection between the pair of side surfaces. In the followingdescription, one of the pair of side surfaces may be referred to as afirst side surface 10 d, and the other may be referred to as a secondside surface 10 d′. Similarly, one of the pair of front surfaces may bereferred to as a first front surface 10 e, and the other may be referredto as a second front surface 10 e′.

FIG. 3 is a top view of the cutting insert 10 from the upper surface 10a. As shown in FIG. 3, a ridge line at which the upper surface 10 a andthe first side surface 10 d intersect is formed in a straight lineshape. Similarly, a ridge line at which the upper surface 10 a and thesecond side surface 10 d′ intersect is formed in a straight line shapeparallel to the ridge line of the first side surface 10 d. As shown inFIG. 3, an interval between the ridge lines, formed in the straight lineshapes, of the first and second side surfaces 10 d and 10 d′ is definedas a width W of the cutting insert 10. The width W of the cutting insert10 is, for example, 4 to 4.5 mm.

In the illustrated example, the lower surface 10 b of the cutting insert10 is formed in a planar shape. A through hole H to penetrate the uppersurface 10 a and the lower surface 10 b is formed in a central part ofthe cutting insert 10. The cutting insert 10 is fixed to a body B byscrewing a clamp screw penetrating the through hole H with a femalescrew provided on a seat surface of the body B of an indexable cuttingtool. In this case, the cutting insert 10 is fixed to the body B suchthat the side surface 10 d side is close to a rotation axis AX of thebody B and the side surface 10 d′ side is far from the rotation axis AXof the body B (see FIG. 9). The body B will be described later in detailwith reference to FIGS. 8 to 10.

FIG. 4 is a side view of the cutting insert 10 from the second sidesurface 10 d′ of the circumferential surfaces. FIG. 5 is a side view ofthe cutting insert 10 from the second front surface 10 e of thecircumferential surfaces. As shown in FIGS. 4 and 5, the circumferentialsurfaces 10 d, 10 d′, 10 e, and 10 e′ of the cutting insert 10 include avertical part 10 h which is connected to the lower surface 10 b andperpendicular to the lower surface 10 b, a connection part 10 j which isconnected to the vertical part 10 h and expands such that across-sectional area thereof parallel to the lower surface 10 bincreases toward a side away from the lower surface 10 b, and aninclined part 10 k which is connected to the connection part 10 j andexpands such that a cross-sectional area thereof parallel to the lowersurface 10 b increases toward a side away from the lower surface 10 b.

In the following description, an angle at which the circumferentialsurfaces are inclined with respect to a central axis of the through holeH is referred to as an inclination angle. In addition, the angle formedbetween the central axis of the through hole H and the circumferentialsurfaces is obtained as a complementary angle of the angle formed by adirection vector of the central axis and a normal vector of thecircumferential surfaces. As shown in FIG. 5, the circumferentialsurfaces 10 d, 10 d′, 10 e, and 10 e′ of the connection part 10 j have alarger inclination angle (a first inclination angle α) than thecircumferential surfaces of the vertical part 10 h. Therefore, anincrease rate of the cross-sectional area is large. On the other hand,the circumferential surfaces of the inclined part 10 k have a smallerinclination angle (a second inclination angle 1) than thecircumferential surfaces of the vertical part 10 h. Therefore, theincrease rate of the cross-sectional area is small.

Further, heights in a direction perpendicular to the lower surface 10 bincrease in the order of the vertical part 10 h, the connection part 10j, and the inclined part 10 k. In addition, a height h3 of the inclinedpart 10 k is larger than a sum h1+h2 of a height h1 of the vertical part10 h and a height h2 of the connection part 10 j.

In other words, the cutting insert 10 has a constricted shape from theupper surface 10 a to the lower surface 10 b, and has a structure inwhich the inclined part 10 k contracts such that the cross-sectionalarea gradually decreases from the upper surface 10 a toward the lowersurface 10 b, the connection part 10 j then contracts such that thecross-sectional area decreases greatly toward the lower surface 10 b,and the vertical part 10 h is connected to the lower surface 10 b whilea constant cross-sectional area is maintained. Also, the inclinationangles of the connection part 10 j and the inclined part 10 k need notbe constant. However, an average value of the inclination angle of theconnection part 10 j and an average value or a representative value ofthe inclination angle of the inclined part 10 k have a magnitudecorrelation therebetween.

As shown in FIGS. 1 and 2, a cutting edge is formed on at least a partof the ridge line at which the upper surface 10 a and the first frontsurface 10 e intersect. The cutting edge includes a corner edge 10 f andan inner cutting edge 10 g. Similarly, the corner edge 10 f and theinner cutting edge 10 g are formed as a cutting edge at the ridge lineat which the upper surface 10 a and the second front surface 10 e′intersect. The cutting insert 10 has a structure that is 180° axiallysymmetric with respect to the center axis of the through hole H. Thatis, the first front surface 10 e and the second front surface 10 e′ havesubstantially the same shape and function. For that reason, the firstfront surface 10 e will be described in detail as a representative, andrepeated descriptions of the second front surface 10 e′ will be omitted.

The corner edge 10 f is provided at a corner part of the cutting insert10 and is formed to have a predetermined curvature when viewed from adirection facing the upper surface 10 a. In other words, the corner edge10 f is formed in an arc shape. The curvature of the corner edge 10 fcan be selected in accordance with a specification of a corner R to bemachined. For example, when the specification of the corner R is 2 mm,the cutting insert 10 in which the corner edge 10 f has a predeterminedradius of curvature (for example, slightly less than 2 mm) may beselected such that the corner R after machining in consideration of arotation locus of the corner edge is 2 mm.

In the present embodiment, as shown in FIG. 3, the corner edge 10 fwhich is larger and has a larger curvature than usual is formed. In theillustrated example, a width Wf of the corner edge 10 f is 40% or moreand 50% or less of the width W of the cutting insert 10 in the directionperpendicular to the rotation axis AX of the body B. More specifically,when viewed from the direction facing the upper surface 10 a, the corneredge 10 f is formed from the side surface 10 d′ to a position of 40% to50% in a direction of the width W (a direction connecting the first sidesurface 10 d and the second side surface 10 d′), and the radius ofcurvature is formed, for example, to be 50% or less of the width W.

In addition, in the example shown in FIGS. 3 and 5, the inner cuttingedge 10 g is formed continuously with the corner edge 10 f. The innercutting edge 10 g includes the other end 12 connected to the corner edge10 f, and one end 11 connected to the first side surface 10 d formedsubstantially linearly when viewed from the direction facing the uppersurface 10 a.

As shown in FIGS. 4 and 5, the upper surface 10 a is formed to be flatand parallel to the lower surface 10 b. In other words, a ridge line ofthe upper surface 10 a including the corner edge 10 f and the innercutting edge 10 g is positioned at substantially the same height fromthe lower surface 10 b over the entire circumference thereof. Morespecifically, the upper surface 10 a has a flat surface 10 p whoseheight (distance) from the lower surface 10 b is constant, and thenegative land 10 q surrounding the flat surface 10 p.

Ridge lines at which the negative land 10 q and the circumferentialsurfaces 10 d, 10 d′, 10 e, and 10 e′ intersect have a height from thelower surface 10 b which is substantially equal to that of the flatsurface 10 p and are slightly lower than the flat surface 10 p. That is,distances from the lower surface 10 b between all parts of the cuttingedges 10 f, 10 g, and 10 m formed on the ridge lines and the uppersurface 10 a are substantially constant. A difference in height betweenthe cutting edge at the highest position from the lower surface 10 b andthe cutting edge at the lowest position from the lower surface 10 b is,for example, 1 mm or less.

In the example shown in FIG. 4, a wiper edge 10 m is formed on a sideopposite to the inner cutting edge 10 g with the corner edge 10 finterposed therebetween. The wiper edge 10 m is formed to be muchshorter than the corner edge 10 f and the inner cutting edge 10 g. Theother end of the wiper edge 10 m is connected to a linear ridge line ofthe upper surface 10 a. The ridge line and the wiper edge 10 m intersectat an obtuse angle of almost 180° at an inner angle.

As shown in FIG. 3, the negative land 10 q having a negative angle (θ1to θ2) is formed adjacent to the cutting edge on the upper surface 10 a.FIG. 6 is a cross-sectional view along line VI-VI in FIG. 3. FIG. 7 is across-sectional view along line VII-VII in FIG. 3. As shown in FIGS. 6and 7, the angle of the negative land 10 q adjacent to the corner edge10 f gradually increases to approach a positive value from one end 12connected to the inner cutting edge 10 g toward the other end 13connected to the wiper edge 10 m.

In the illustrated example, an angle θ1 of the negative land 10 q at theend 12 on the inner cutting edge 10 g side shown in FIG. 6 is −20°. Theangle of the negative land 10 q gradually increases from θ1 toward theend 13 connected to the wiper edge 10 m. An angle θ2 of the negativeland 10 q at the end 13 on the wiper edge 10 m side shown in FIG. 7 is−8°.

In addition, the upper surface 10 a is configured of the flat surface 10p, in which a chip breaker or the like is not formed, in most of theportion excluding the through hole H and the negative land 10 q. Aproportion of the flat surface 10 p to the upper surface 10 a is 90% ormore.

FIG. 8 is a perspective view showing an example of an end mill E onwhich two cutting inserts 10 are mounted, FIG. 9 is a diagram of a tippart of the end mill E, including the tip and the vicinity thereof, whenviewed from a direction perpendicular to the rotation axis AX, and FIG.10 is a diagram of the tip part of the end mill E when viewed from thedirection of the rotation axis AX. The end mill E is an example of theindexable cutting tool. The end mill E shown in FIGS. 8 to 10 is asmall-diameter end mill E having a tool diameter of 8 mm to 20 mm andcan be used, for example, for machining a mold.

As shown in FIGS. 8 to 10, two seat surfaces F and F′ for mounting thecutting inserts 10 are formed on a cylindrical body B at the tip part ofthe end mill E. Female screws are formed in the seat surfaces F and F′.By screwing a clamp screw CS penetrating the through hole H of thecutting insert 10 with the female screw, the lower surface 10 b of thecutting insert 10 is pressed against each of the seat surfaces F and F′,and each cutting insert 10 is fixed to the body B. A base end of the endmill E opposite to the tip part is fixed to a machine tool (not shown).

In this case, the front surface 10 e faces in the same direction as therotation axis AX. As described above, the cutting insert 10 is mountedon the body B such that the side surface 10 d is close to the rotationaxis AX and the side surface 10 d′ is far from the rotation axis AX.Therefore, the corner edge 10 f and the inner cutting edge 10 g arepresent from an outer circumferential side toward a center of the endmill E.

Hereinafter, a structure for increasing rigidity of the body B will bedescribed. The cutting insert 10 according to the present embodimentcontributes to increasing the rigidity of the body B. Since the width Wof the cutting insert 10 is extremely thin, that is, 4 to 4.5 mm, thebody B on which the cutting insert 10 is mounted is also thin. As avolume of the body B decreases, the rigidity of the body B alsodecreases.

In addition, in order to securely bring the side surface of the cuttinginsert into contact with a wall surface of a tip seat of the body whenthe cutting insert is mounted on the body, a relief (a recessed part) isformed around a corner part connecting the seat surface and the wallsurface of the tip seat. The inventors of the present application havefocused on the point that removing the corner part of the tip seat toform the relief has an effect on the rigidity of the body.

Since the cutting insert 10 according to the present embodiment isprovided with the inclined part 10 k and the connection part 10 j, anedge of the lower surface 10 b is moved toward a center side of thelower surface 10 b as compared with a typical cutting insert in whichthe inclined part 10 k and the connection part 10 j are not provided.For this reason, as shown in FIG. 10, it is possible to reduce therelief formed at each of corner parts C and C′ of the tip seat of thebody B on which the cutting insert 10 is mounted, that is, to increase across-sectional area of the body B. Therefore, the rigidity of the bodyB can be increased.

Further, since the width W of the cutting insert 10 is very narrow, thatis, 4 to 4.5 mm, each contact area of the seat surface F and the seatsurface F′ of the tip seat is also restricted. When the contact area istoo small, the cutting insert cannot be stably mounted on the body B.Since the cutting insert 10 is provided with the vertical part 10 hfollowing the inclined part 10 k, an area of the lower surface 10 b canbe increased as compared with a case in which there is no vertical part10 h. Therefore, a large contact area of the cutting insert with each ofthe seat surface F and the seat surface F′ of the chip seat can besecured.

Also, since a circumferential surface of the inclined part 10 k having arelatively small inclination angle can be brought into contact with thewall surface of the tip seat, the cutting insert 10 can be supportedmore stably as compared with a case in which a circumferential surfacehaving a large inclination angle is brought into contact with the wallsurface of the tip seat. Therefore, the cutting insert 10 according tothe present embodiment can achieve both improvement in rigidity of thebody B and stable mounting.

Next, effects of the present embodiment will be described. The angle (θ1to θ2) of the negative land 10 q formed adjacent to the corner edge 10 fhas a smaller value (for example, θ1) at a portion located closer to thetip of the milling tool. By providing the negative land of which theland angle gradually changes to a positive side toward a side away fromthe tip of the milling tool, cutting edge strength can be enhanced whilechip evacuation can be improved.

As a second (secondary) effect of the present embodiment, the cuttinginsert 10 is disposed on the tool body B to form a positive axial rakeangle, and accordingly, in the case of cutting a work material that isnot a hard material, if the cutting insert 10 is replaced such that therake angle becomes a positive angle, the tool body B can be shared incutting of a high-hardness material and cutting of other work materials.

In addition, since the wiper edge 10 m is connected to the corner edge10 f, roughness of a machined surface of a standing wall is improved.Since the linear ridge line connected to the wiper edge 10 m and thewiper edge 10 m intersect at an obtuse angle, contact of the linearridge line with a workpiece is avoided. Therefore, it is possible toprevent a situation in which the linear ridge line comes into contactwith a work surface and deteriorates roughness of the machined surface.

Further, grooves and irregularities such as a chip breaker are notformed on the upper surface 10 a, and most of the upper surface 10 a isformed of the flat surface 10 p. Accordingly, when the negative land 10q is formed by grinding, a degree of freedom in moving a grindstoneincreases, and manufacturing costs decrease. That is, the cutting insert10 can be manufactured with higher precision than a cutting inserthaving a complicated shape on which a chip breaker or the like isformed.

The present invention can be variously modified without departing fromthe gist thereof. For example, some components of one embodiment may becombined with other embodiments within a range of an ordinary creativityof those skilled in the art.

What is claimed is:
 1. A cutting insert which is to be mounted on a bodyrotating around a rotation axis and constitutes an indexable cuttingtool together with the body, the cutting insert comprising a lowersurface mounted on a seat surface of the body, an upper surface oppositeto the lower surface, and a circumferential surface connecting the lowersurface to the upper surface, wherein a cutting edge is formed at aridge line at which the upper surface and the circumferential surfaceintersect, the cutting edge including an inner cutting edge and a corneredge, the corner edge is formed at a position farther from the rotationaxis than the inner cutting edge and connected to the inner cuttingedge, the corner edge being formed in an arc shape in a plan view from adirection facing the upper surface and having a width of 40% or more and50% or less of a width of the cutting insert in a directionperpendicular to the rotation axis, the upper surface includes anegative land which is formed along the cutting edge and has a negativeangle, and a flat surface which is connected to the negative land andparallel to the lower surface, and the angle of the negative landincreases from one end of both ends of the corner edge, the one endbeing connected to the inner cutting edge, toward the other end.
 2. Thecutting insert according to claim 1, wherein the cutting edge furtherincludes a linear wiper edge which is connected to the corner edge andparallel to the rotation axis, and in the ridge line in the wiper edge,a linear ridge line of the upper surface intersects the wiper edge at anobtuse angle.
 3. The cutting insert according to claim 1, wherein thecutting insert further includes a through hole penetrating from theupper surface to the lower surface, and when the upper surface is viewedfrom above, a proportion of the flat surface in an area excluding thethrough hole from the upper surface is 90% or more.
 4. The cuttinginsert according to claim 2, wherein the cutting insert further includesa through hole penetrating from the upper surface to the lower surface,and when the upper surface is viewed from above, a proportion of theflat surface in an area excluding the through hole from the uppersurface is 90% or more.